The present invention is in the field of sealing apparatus and method for use in a turbine engine. More particularly the present invention relates to a seal structure employed in a turbine engine wherein the engine includes a centrifugal compressor receiving ambient air and pressurizing this ambient air for delivery to a combustor and a turbine disposed in back-to-back relationship with the compressor and receiving combustion products formed by combustion of a fuel in the pressurized air supplied by the compressor. Historically such turbine engines have employed a disk-like centrifugal compressor rotor and a similar disk-like radial inflow turbine disposed in back-to-back relationships such that they cooperatively define therebetween a radially inwardly extending annular groove. At the radially inner extent of the annular groove the turbine and compressor rotors cooperatively carry a seal runner, or centering ring, which served as a concentricity maintaining structure with respect to the turbine and compressor rotors respectively.
A housing structure of the turbine engine conventionally carries a disk-like annular seal member extending radially inwardly into the annular groove between the compressor rotor and turbine rotor, and at its radially inner extent carrying a seal structure. The seal structure may be, perhaps, of a labyrinth type, sealingly engaging the seal runner which is carried cooperatively by the compressor rotor and turbine rotor. Generally speaking, these conventional seal structures were made of sheet metal stampings of comparatively light gage and have been subject to a variety of shortcomings because of their structural nature.
By way of example, the annular sealing structure is subjected to an axial force because of the fluid pressure differential thereacross existing between the discharge of the centrifugal compressor and the inlet pressure at the radial inflow turbine. This pressure differential causes the relatively flexible conventional sheet metal seal structure to be displaced axially in a direction towards the turbine rotor. Additionally the seal structure is subjected to a radial temperature differential resulting from the flow of hot gasses radially inwardly and across the turbine rotor. The hot gas flow provides a heating input to the annular seal structure which is most pronounced at its radially outer extent and decreases progressively radially inwardly therefrom. On the other hand the seal structure is subjected to a comparative cooling effect on the compressor side thereof as a result of the small portion of compressor discharge airflow which circulates in the backspace between the compressor rotor and the adjacent face of the annular seal structure. Because of this differential radial heating and cooling on opposite faces of the seal structure, conventional seal structures have displayed a warping or buckling similar to that experienced with the bottom of a frying pan which is heated most intensely in the center and is cooler at its outer periphery.
Such seal structures, due to this differential thermal expansion experienced in the radial direction of the structure, will in one location warp in one axial direction and in an adjacent location may warp or displace in the opposite axial direction. In the case of the conventional annular seal structure such warping and displacements superimposed upon the axial displacements which resulted from differential pressures across the seal structure results in axial as well as radial movements at the center opening of the seal structure whereat sealing integrity is to be maintained.
Further, the heat input to the seal structure may be circumferentially nonuniform. Thus, the seal structure will have a nonuniform circumferential and radial temperature distribution. This circumferentially nonuniform temperature distribution further contributes to warping of the seal structure. As a result, the labyrinth or other conventional seal structure which is carried at the center opening of the interstage seal is displaced axially as well as radially and sealing integrity is generally not successfully maintained by conventional interstage seals of the type described above.
A result of the axial, radial, and warping displacements experienced by conventional seal structures has been the necessity to provide larger than desired clearances between the turbine back face and the seal structure. Consequently, a portion of the combustion products flowing radially inwardly onto the turbine are lost into the excessive clearance provided at the seal structure. Turbine efficiency is adversely affected by this loss of a portion of the combustion products. Also, the heat input to the seal structure is increased as energy input to and efficiency of the turbine is decreased by excessive seal assembly clearances.
Accordingly, it is an object for the present invention to provide a seal assembly of the type described which resists axial, radial, and warping displacements; and which also allows decreased turbine back face clearances.
The present invention realizes the objects thereof by providing an improved seal structure for a turbine engine, said turbine engine including a housing, said housing rotatably receiving a centrifugal compressor having a rotor, said compressor inducting air via an inlet to said compressor and delivering this air pressurized to an outlet therefrom, a radial inflow turbine including a turbine rotor receiving motive fluid via an inlet of said turbine and expanding said motive fluid toward ambient to extract rotary shaft power therefrom, said compressor rotor and said turbine rotor being disposed in back-to-back relation so that inlet flow to said compressor and outlet flow from said turbine flow in a single axial direction, said turbine rotor being drivingly connected with said compressor rotor and axially spaced therefrom to define a radially inwardly and axially extending annular gap therebetween, said housing carrying and sealingly cooperating with an annular sealing member extending radially inwardly into said gap and at a radially inner extent thereof sealingly cooperating with a radially outwardly disposed cylindrical rotor surface intermediate said compressor rotor and said turbine rotor to substantially prevent air flow from the former toward the latter; said annular sealing member including a radially outer annular rim portion sealingly cooperating with said housing, a first annular wall portion extending radially inwardly and in a first axial direction from said rim portion, a second annular wall portion joining with said first annular portion and extending radially inwardly therefrom and in a second axial direction opposite said first axial direction, and a third annular wall portion joining with said second annular portion and extending radially inwardly therefrom to at its radially inner extent define a bore surface in sealing juxtaposition with said cylindrical rotor surface.